Utilization of synthetic herbicides not only prevents economic loss in food production, but also improves quality of crop products (Gianessi, L. P.; Reigner, N. P. The value of herbicides in U.S. crop production, Weed Technol. 2007, 21, 559-566). However, the use of synthetic herbicides may cause side-effects on environment and human health (Solomon, G. M.; and Schettler, T. Environment and health: 6. Endocrine disruption and potential human health implications, CMAJ, 2000, 163, 1471-1476; Stillerman, K. P.; Mattison, D. R.; Giudice, L. C.; Woodruff, T. J. Environmental exposures and adverse pregnancy outcomes: A review of the science. Reproductive Sci. 2008, 15, 631-650) except that it also leads to an increasing resistance among many weed species (Whaley, C. M.; Wilson, H. P.; Westwood, J. H. A new mutation in plant ALS confers resistance to five classes of ALS-inhibiting herbicides, Weed Sci. 2007, 55, 83-90). Therefore, it is very necessary to develop alternative means for weed management that are eco-friendly, cost-effective and bio-efficacious (Duke, S. O.; Dayan, F. E.; Rimando, A. M.; Schrader, K. K.; Aliotta, G.; Oliva, A.; Romagni, J. G. Chemicals from nature for weed management. Weed Sci. 2002, 50, 138-151).
The use of natural phytochemicals is one of these alternative means (Batish, D. R.; Setia, N.; Singh, H. P.; Kohli, R. K. Phytotoxicity of lemon-scented eucalypt oil and its potential use as a bioherbicide, Crop Protection, 2004, 23, 1209-1214). Due to allelopathic properties, many of these chemicals are either released in air or soil to kill neighboring weeds or to inhibit their germination and/or growth. These phytotoxic chemicals include phenolic compounds (e.g., catechin, ellagic acid, sorgoleone, juglone, ceratiolin, usnic acid), terpenoids (e.g., 1,8-cineole, geranial, neral, cinmethylin, solstitiolide), quassinoids (e.g., ailanthone, chaparrine, ailanthinol B), benzoxazinoids (e.g., hydroxamic acids), glucoinolates (e.g., glucohirsutin, hirsutin, arabin), and some amino acids such as meta-tyrosine (Macias, F. A.; Molinillo, J. M. G.; Varela, R. M.; Galindo, J. C. J. Allelopathy—a natural alternative for weed control. Pest Manag Sci., 2007, 63, 327-348; Bertin, C.; Weston, L. A.; Huang, T.; Jander, G.; Owens, T.; Meinwald, J.; Schroeder, F. C. Grass roots chemistry: meta-Tyrosine, an herbicidal nonprotein amino acid. PNAS, 2007, 104, 16964-16969). Commercially available herbicides include products based on clove oil, lemongrass oil and d-limonene.
The Genus Piper 
The genus Piper in the Piperaceae family contains approximately 2000 species found primarily in tropical regions. Plants of this genus are normally slender aromatic climbers with perennial woody roots. The fruits commonly known as “pippali” in India and “Bi Bo” in China are used as a spice and also as a preservative in pickles. They are also used as cattle feed.
In traditional medicinal practice, P. longum fruits have been advocated to be beneficial in treatment of diseases such as gonorrhea, menstrual pain, tuberculosis, sleeping problems, respiratory tract infections, chronic gut-related pain, and arthritic conditions (Krishnamurthi, A. 1969. The Wealth of India Raw Materials, vol. 8. CSIR, New Delhi, India, p. 96; Ghoshal, S.; Prasad, B. N. K.; Lakshmi, V. Antiamoebic activity of Piper longum fruits against Entamoeba histolytica in vitro and in vivo, J. Ethanopharmacol. 1996, 50, 167-170; Choi, E. M.; Hwang, J. K. Investigations of anti-inflammatory and antinociceptive activities of Piper cubeba, Physalis angulata and Rosa hybrid, J. Ethanopharmacol. 2003, 89, 171-175, Mata, R.; Morales, I.; Perez, O.; Rivero-Cruz, I.; Acevedo, L.; Enriquez-Mendoza, I.; Bye, R.; Franzblau, S.; Timmermann, B. Antimycobacterial compounds from Piper sanctum, J. Nat. Prod. 2004, 67, 1961-1968). Other reported beneficial effects of P. longum include analgesic and diuretic effects, relaxation of muscle tension, and alleviation of anxiety (Vedhanayaki, G.; Shastri, G. V.; Kuruvilla, A. Analgesic activity of Piper longum Linn. Root, Ind. J. Exp. Biol. 2003, 41, 649-651; Das, Biswanath, D.; Kashinatham, A.; Srinivas, K. V. N. S. Alkamides and other constituents of Piper longum, Planta Med, 1996, 62, 582). In addition, pipernonaline from P. longum has been found to possess mosquito larvicidal activity (Yang, Y. C.; Lee, S. G.; Lee, H. K.; Kim, M. K.; Lee, S. H.; Lee, H. S. A piperidine amide extracted from Piper longum L. fruit shows activity against Aedes aegypti Mosquito Larvae, J. Agric. Food Chem., 2002, 50, 3765-3767).
An alkaloid has been isolated from Piper nigrum (pepper) which is an alkenylene piperidine amide containing a C18 alkenylene with two or more double bonds. This compound has been found to inhibit mycotoxin biosynthesis. (U.S. Pat. No. 6,825,216).
Sarmentine
N-(2E,4E-Decadienoyl)pyrrolidine (also called sarmentine) was originally separated from the fruit of Piper sarmentosum in 1987 [Likhitwitayawuid, K., Ruangrungsi, N, Lange, G. and Decicco, C., Structural Elucidation and Synthesis of New Components isolated from Piper Samentosum, Tetrahedron 1987 (43) 3689-3694] and also from Piper nigrum in 1988 [Kiuchi, F., Nakamura, N., Tsuda, Y., Kondo, K. and Yoshimura, H. Studies on Crude Drugs Effective on Visceral Larva Migrans. IV. Isolation and Identification of Larvicidal Principles in Pepper Chemical and Pharmaceutical Bulletin 1988 (36):2452], and first synthesized in 1995 [Bernabeu, M., Chinchilla, R. and Najera, C., (2E,4E)-5-Tosyl-2,4-pentadienamides: New Dienic Sulfones for the Stereoselective Synthesis of (2E,4E)-Dienamides, Tetrahedron Letter, 1995 (36) 3901-3904]. Sarmentine has been found to be in vivo skin antioxidant protecting photoaged skin [Cornacchione, S.; Sadick, N. S.; Neveu, M.; Talbourdet, S.; Lazou, K.; Viron, C.; Renimel, I.; de Quéral, D.; Kurfurst, R.; Schnebert, S.; Heusèle, C.; André, P.; Perrier E. In vivo skin antioxidant effect of a new combination based on a specific Vitis vinifera shoots extract and a biotechnological extract. J. Drugs in Dermatol. 2007, 6S, 8-13], display antiplatelet aggregation activity [Li, C. Y.; Tsai, W.; Damu, A. G.; Lee, E. J.; Wu, T. S.; Dung. N. X.; Thang, T. D.; Thanh, L. Isolation and identification of antiplatelet aggregatory principles from the leaves of Piper lolot, J. Agric. Food Chem. 2007, 55, 9436-9442], antiplasmodial and antimycobacterial activities [Tuntiwachwuttikul, P.; Phansa, P.; Pootaeng-on, Y.; Taylor, W. C. Chemical constituents of the roots of Piper Sarmentosum, Chem. Pharm. Bull. 2006, 54, 149-151] and antituberculosis activity [Rukachaisirikul, T.; Siriwattanakit, P.; Sukcharoenphol, K.; Wongvein, C.; Ruttanaweang, P.; Wongwattanavuch, P.; Suksamrarn, A. Chemical constituents and bioactivity of Piper sarmentosum, J. Ethnopharmacol., 2004, 93, 173-176]. Sarmentine is used as a solubilizer of hydrophobic compounds in cosmetics and pharmaceuticals (Stephen, T.; Andrew, H. Compositions comprising macromolecular assembles of lipid surfactant, PCT Publication No. WO/2008/065451).